How much of an effect does delaying processing have on final image colours?

I ship my rolls to Tokyo from Australia for processing, so I usually shoot a couple & send together to save on postage etc. I keep all of them refrigerated, most of the time even between exposing unfinished rolls again, plus all of my negative stock and reversal stock is kept in cold storage.

The thing is, I don't shoot THAT often, sometimes completing a 40ft Single 8 roll over 2 or 3 weeks. Then shipping can take over a week. I'm just curious, but in the end I will continue to send to Japan, as it's cheaper with included processing taking into account bulk shipping and return, than shooting on Super 8 and getting processed in Australia, especially now that Kodak has increased prices...

So, if anyone has knowledge on delaying processing, staying on topic with that, I'd love to hear from experienced shooters

I usually send film batches to processing about every 4 - 5 months or so and the results are usually very good. This is for 16mm and 35mm film however and I keep the exposed films in a fridge. Moisture has never been a problem but I am very careful with the rolls and always keep them in stable temperature.

One batch waited about 1.5 years after exposure before I got it developed and it had horrible base grain levels and a little dimmer colours but otherwise it was quite OK. (N16mm 8663 and 7219)

I usually send film batches to processing about every 4 - 5 months or so and the results are usually very good. This is for 16mm and 35mm film however and I keep the exposed films in a fridge. Moisture has never been a problem but I am very careful with the rolls and always keep them in stable temperature.

One batch waited about 1.5 years after exposure before I got it developed and it had horrible base grain levels and a little dimmer colours but otherwise it was quite OK. (N16mm 8663 and 7219)

Which had little to with you keeping the film too long. Either it was already extremely expired or processing f-ed up.

People find 20 year old find and have these processed into perfectly good images.

The faster the film, the more gamma-ray fogging will accumulate even if stored at -18°C as we do with sensitometric control strips. At six months after exposure we see a marked increase in blue fog level on 200 ISO. 50 ISO would be much more stable, 500 ISO much less. Process your film as soon as practical, keeping it cool in the meantime.